FIELD OF THE INVENTION
[0001] This invention relates generally to electrostatographic printing machine, and, more
particularly, concerns an image-on-image multicolor printing machine, wherein individual
imaging and developer bias voltages are selectively and systematically adjusted as
a function of residual, or non-uniform background charge potentials on an imaging
member for preventing the development thereof in subsequent image development steps.
BACKGROUND OF THE INVENTION
[0002] In order to produce multicolor output images, electrostatographic printing machines
generally utilize a so-called subtractive color mixing, whereby multicolor images
are created from three colors, namely cyan, magenta and yellow, which are complementary
to the three primary colors having light progressively subtracted from white light.
In the case of electrostatographic printing machines, various methods can be utilized
to produce a full process color image using cyan, magenta, and yellow toner images.
[0003] One exemplary method for producing multicolor images of particular interest to the
present invention is known as the Recharge, Expose, and Development (REaD) Image-On-Image
(IOI)process This process involves depositing different color toner layers in superimposed
registration with one another on a photoconductive surface (or other recording medium)
to create a multilayered composite multicolor developed image. In this process, an
initial latent image corresponding to the subtractive color of a developing material
present at a first development station is recorded on the recording medium and the
image is developed. Thereafter, the recording medium having the first developed image
thereon may be recharged and re-exposed to record a latent image thereon corresponding
to another subtractive primary color and developed once again with a second developing
material of appropriate color. The process is repeated until all the different color
developing material layers are deposited in superimposed registration with one another
on the recording medium. The multilayered composite image may then be transferred
from the surface of the recording medium to a copy sheet or other support substrate
and affixed thereto to provide the multicolor print output. Variations on this of
generating and developing a first latent image and subsequently generating and developing
additional images over the first developed image to superimpose a plurality of developed
images on one another are well known in the art, and may make advantageous use of
the present invention. For example, the REaD process may be modified for ionographic
processes by implementing an image generation and develop process since uniform charging
or recharging of the recording medium are not required, but rather image generation
via an ionographic writing head sprays ions in image configuration onto the recording
medium in ionographic processes. One commercial embodiment of such a system is provided
in the 8900 series machines manufactured by Xerox Corporation.
[0004] Using the typical electrostatographic printing process as an example, the REaD color
process described hereinabove may be implemented via either of two architectures:
a single pass, single transfer architecture, wherein multiple imaging stations, each
comprising a charging unit, an imaging device, and a developing unit, are situated
about a single photoconductive belt or drum; or a multipass, single transfer architecture,
wherein a single imaging station comprising the charging unit, an imaging device,
and multiple developer units are located about a photoconductive belt or drum. As
the names imply, the single pass architecture requires a single revolution of the
photoconductive belt or drum to produce a color image, while the multipass architecture
requires multiple revolutions of the photoconductive belt or drum to produce the color
print or copy. Various other processes and systems have been successfully implemented,
wherein each color separation is imaged and developed in sequence such that each developing
station (except the first developing station) must apply developing material to an
electrostatic latent image over areas where a previous latent image has been developed.
[0005] One significant problem which has arisen in systems where sequential development
occurs over previously developed images for producing a multicolor image is that the
surface charge of one latent image may not be completely neutralized by the toner
particles deposited thereon during a corresponding development cycle. In CAD ionography,
if the electrostatic image of one color separation is not completely discharged by
toner particles during a development cycle, that electrostatic image can attract toner
of another color during a subsequent developing cycle. Similarly, in REaD processes,
during the process step wherein a photoconductor is recharged to prepare the surface
thereof for a subsequent imaging cycle, the recharge process step may generate a non-uniform
charge potential on the photoreceptor due to the presence of previously developed
images This non-uniform charge potential results in a non-uniform background potential
which will be developed during a subsequent development step. Likewise, exposure and/or
imaging steps may result in non-uniform discharging of the recording medium, generating
non-uniform background charge potentials that may be undesirably or erroneously developed
during subsequent development steps.
[0006] Thus, various circumstances may arise in image-on-image electrostatographic printing
processes, wherein residual charge potentials may remain on the recording medium after
a previous development step, or non-uniform background potentials may be generated
which will, in turn, be developed by another color in a subsequent development step.
This phenomenon is known as overplating or image staining, wherein a second process
color erroneously develops non-imaging areas in regions which should not be developed
during that process step. See, for additional explanation of the problem, R. M. Schaffert,
Electrophotography (London: Focal Press, 1975), at pp. 184-186.
[0007] Many schemes have been advanced to overcome the problem of overplating. For example,
in U. S. Pat. No. 4,701,387 to Alexandrovich et al., the problem of residual image
development is discussed, wherein a proposed solution is described for rinsing the
developed surface with a polar liquid after each development step. It is suggested
that application of a polar rinse liquid neutralizes and solvates residual counter-ions
deriving from charge control agents and stabilizers present in the liquid developer.
While the Alexandrovich et al. method may be effective in reducing the staining problem,
such a multiple washing procedure is time consuming and, therefore, may be unacceptable.
[0008] Other schemes have been proposed in the art with the purpose of preventing toner
particles previously deposited on a latent image from flying back to the development
apparatus. For instance, to this end, US-A-4 629 669, suggest a multicolor printing
system wherein increasing bias voltages are applied to the development apparatuses
as later steps are performed.
[0009] The present invention contemplates an apparatus and process for eliminating overplating
or staining by controlling electrical bias voltages applied in imaging and/or development
steps of a typical electrostatographic printing process to substantially prevent the
overplating problem. Thus, in accordance with the present invention, a scheme for
selectively controlling bias voltages applied to each individual imaging development
system present in the overall multi-color printing system as a function of the properties,
such as the background or residual voltage associated with a residual image on the
recording medium is disclosed such that the imaging and developing bias of a given
color is dependent on the performance of the previous color development and/or recharge
and/or imaging steps.
SUMMARY OF THE INVENTION
[0010] In accordance with one aspect of the present invention, there is provided an electrostatographic
printing machine for producing a multicolor output image from an input image signal,
comprising: a recording medium adapted to have a plurality of latent electrostatic
images recorded thereon, defined by image charge potential areas and background charge
potential areas; a first image device for generating a first electrostatic latent
image on the recording medium corresponding to a first color separation of the input
image signal; a first development apparatus for developing the first electrostatic
latent image on the recording medium by deposing charged developing material or said
electrostatic first latent image so as to produce a first developed image thereon;
a second imaging device for generating a second electrostatic latent image on the
recording medium corresponding to a second color separation of the input image, the
second electrostatic latent image being superimposed on the first developed image
on the recording medium; a second development apparatus for developing the second
electrostatic latent image on the recording medium by deposing charged developing
material on said electrostatic second latent image so as to produce a second developed
image thereon; and means for setting said second development apparatus to a voltage
that is substantially equal to or greater than the charge potential in the background
areas on the recording medium to substantially prevent development thereof.
[0011] In accordance with another aspect of the present invention, there is provided an
electrostatographic printing process for producing a multicolor output image from
an output image signal, comprising the steps of: providing a recording medium adapted
to have a plurality of latent electrostatic images recorded thereon defined by image
charge potential areas and background charge potential areas; generating a first electrostatic
latent image on the recording medium corresponding to a first color separation of
the input image; developing the first electrostatic latent image on the recording
medium by deposing charged developing material on said first electrostatic latent
image by means of a first development apparatus so as to produce a first developed
image thereon; generating a second electrostatic latent image on the recording medium
corresponding to a second color separation of the input image, the second electrostatic
latent image being superimposed on the first developed image on the recording medium;
developing the second electrostatic latent image on the recording medium by deposing
charged developing material on said second electrostatic latent image by means of
a second development apparatus so as to produce a second developed image thereon;
setting said second development apparatus during said image generating steps to a
voltage that is substantially equal to or greater than the charge potential in the
background areas on the recording medium to substantially prevent development thereof.
FIG. 1 is a schematic, elevational view of an exemplary color electrostatographic
printing system, incorporating the electrical biasing scheme for eliminating overplating
or image staining in accordance with the present invention; and
FIG. 2 is a schematic, elevational view of an exemplary ionographic printing system
incorporating electrical biasing scheme for eliminating overplating or image staining
in accordance with the present invention.
[0012] For a general understanding of the features of the present invention, reference is
made to the drawings, wherein like reference numerals have been used throughout to
designate identical elements. FIG. 1 is a schematic elevational view illustrating
an exemplary full-color electrostatographic printing machine incorporating the features
of the present invention. Inasmuch as the art of electrostatographic printing is well
known, the various processing stations employed in the printing machine of FIG. 1
will be described briefly prior to describing the invention in detail. It will become
apparent from the following discussion that the apparatus of the present invention
may be equally well suited for use in a wide variety of printing machines and is not
necessarily limited in its application to the particular electrostatographic machine
described herein. For example, it will be expressly understood that the method and
apparatus of the present invention may find application in a dry toner-type electrostatographic
printing machine, a liquid developing material-type electrostatographic printing machine
as well as dry or liquid ionographic printing apparatus. Moreover, while the present
invention will hereinafter be described in connection with a preferred embodiment
thereof, it will be understood that the description of the invention is not intended
to limit the invention to this preferred embodiment. On the contrary, the description
is intended to cover all alternatives, modifications, and equivalents as may be included
within the spirit and scope of the invention as defined by the appended claims.
[0013] Turning now to FIG. 1, a multicolor electrostatographic printing machine is shown,
incorporating the features of the present invention therein. The printing machine
employs a photoreceptive belt 18 which comprises a mutilayered structure, including
a photoconductive surface deposited on an electrically grounded conductive substrate,
wherein the photoconductive surface is preferably made from a selenium alloy and the
conductive substrate is preferably made from an aluminum alloy. The photoreceptive
belt 18 is rotated along a curvilinear path defined by rollers 12 and 14 for sequentially
advancing successive portions of the belt through the various processing stations
disposed about the path of belt movement. As such, roller 12 is preferably rotatably
driven in the direction of arrow 13 by a suitable motor and drive system (not shown)
with roll 14 likewise rotating in the direction of arrow 13, thereby advancing belt
18 in the direction of arrow 16.
[0014] Initially, the belt 18 passes through a charging station, where a corona generating
device 20 applies an electrical charge potential to the photoconductive surface of
belt 18, placing a relatively high, substantially uniform potential thereon.
[0015] After the substantially uniform charge is placed on the photoreceptive surface of
the belt 18, the electrostatographic printing process proceeds by imaging an input
document (or by providing a computer generated image exposure signal) for discharging
the photoconductive surface in image configuration according to the image to be generated.
In this process step, the charge previously placed on the photoreceptor is selectively
discharged to generate a latent electrostatic image corresponding to the desired output
image. This imaging process may be accomplished by various techniques, and is most
commonly accomplished by either projecting a reflected light image on to the photoreceptor
to discharge non-image areas thereon, or by selectively exposing the photoreceptor
to a light source in accordance with a computer generated modulation signal.
[0016] For multicolor printing and copying, the imaging process involves separating the
imaging information into the three primary colors to provide a series of subtractive
imaging signals, wherein each of the separate imaging signals is proportional to the
intensity of the incident light of each of the primary colors. These imaging signals
are then transmitted to a series of individual imaging elements 22, 32, 42 and 52,
which may include a raster output scanner (ROS) or an LED array for generating complementary
color separated latent images on the charged photoreceptive belt 18. Typically, each
imaging element 22, 32, 42 and 52 writes the latent image information in a pixel by
pixel manner.
[0017] In the exemplary electrostatographic system of FIG. 1, each of the color separated
electrostatic latent images are serially developed on the photoreceptive belt 18 via
a donor roll developing apparatus 24, 34, 44 and 54. Each developing apparatus transports
a different color developing material into contact with the electrostatic latent image
on the photoreceptor surface so as to develop the latent image with pigmented toner
particles to create a visible image. By way of example, developing apparatus 24 transports
cyan colored developer material, developing apparatus 34 transports magenta colored
developer material, developing apparatus 44 transports yellow colored developer material,
and developing apparatus 54 transports black colored developer material. Each different
color developing material comprises pigmented toner particles, wherein the toner particles
are charged to a polarity opposite in polarity to the latent image on the photoconductive
surface of belt 18 such that the toner particles are attracted to the electrostatic
latent image to create a visible developed image thereof.
[0018] In a typical donor roll developing apparatus, a donor roll 25, 35, 45 or 55 is coated
with a layer of appropriately colored developer material, and is rotated to transport
the toner to the surface of belt 18, where the latent image on the surface of belt
18 image. The developer donor roll is typically electrically biased to a suitable
magnitude and polarity for enhancing the attraction of the toner particles to the
latent image and for preventing the transfer of toner particles on non-image areas.
Each of the developer units 24, 34, 44 and 54 are substantially identical to one another
and represent only one of various known apparatus that can be utilized to apply developing
material to the photoconductive surface or any other type of recording medium. Moreover,
it will be recognized that the present description is directed to a general description
of a multicolor printing system into which the present invention may be incorporated.
It will also be recognized that the development systems described herein may include
additional subsystems such as, for example, an image conditioning system as described
in commonly assigned U.S. Pat. No. 5,570,173, among numerous additional subsystems
as described in various patents and publications available to one of skill in the
art.
[0019] In an exemplary embodiment, the first color separated electrostatic latent image
is developed at developing station 24 using cyan colored developer material. Thereafter,
the photoreceptor belt 18 continues to advance in the direction of arrow 16 to an
optional metering station 28 which may be provided for reducing the thickness of the
developed image on the surface of the photoreceptor. The developed image is then advanced
to a subsequent charging station whereat corona generating device 30 recharges the
photoconductor having the developed image thereon to a substantially uniform charge
potential. Thereafter, imaging element 32 selectively dissipates the charge laid down
by corotron 30 to record a second color separated electrostatic latent image corresponding
to regions to be developed with a magenta developer material. This color separated
electrostatic latent image may be totally or partially superimposed on the cyan image
previously developed on the photoconductive surface of belt 18. This electrostatic
latent image is now advanced to the next successive developing apparatus 34 which
deposits magenta toner thereon.
[0020] After the electrostatic latent image has been developed with magenta toner, the photoconductive
surface of belt 18 continues to be advanced in the direction of arrow 16 to the next
metering station 38 and onward to corona generating device 40, which, once again,
charges the photoconductive surface to a substantially uniform potential. Thereafter,
imaging element 42 selectively discharges this new charge potential on the photoconductive
surface to record yet another color separated electrostatic latent image, which may
be partially or totally superimposed on the prior cyan and magenta developed images,
for development with yellow toner. In this manner, a yellow toner image is formed
on the photoconductive surface of belt 18 in superimposed registration with the previously
developed cyan and magenta images. It will be understood that the color of the toner
particles at each development station may be provided in an arrangement and sequence
that is different than described herein.
[0021] Next, the belt 18 continues to advance to the next metering station 48 and onward
to recharge station 50 and corresponding ROS 52 for selectively discharging those
portions of belt 18 which are to be developed with black toner. In one embodiment,
this final black development step, the developed image is located only on those portions
of the photoconductive surface adapted to have black in the printed page and is not
superimposed over the prior cyan, magenta, and yellow developed images, through a
process known as black undercolor removal.
[0022] The final composite multicolor developed image is next advanced to a transfer station,
where a sheet of support material 100, such as paper or some similar copy substrate,
is advanced from a stack 102 by a feed roll 104. The sheet advances through a chute
106 and is guided to the transfer station, where a corona generating device 108 sprays
ions onto the back side of the paper 100 for attracting the composite multicolor developed
image on belt 18 to the sheet of support material 100. While an electrostatic transfer
process has been described, it will be recognized that various other transfer methods
are known in the art, including mechanical and heat activated processes, which may
be utilized to achieve transfer in the presently described apparatus. In addition,
while direct transfer of the composite multicolor developed image to a sheet of paper
has been described, one skilled in the art will appreciate that the developed image
may be transferred to an intermediate member, such as a belt or drum, and then, subsequently,
transferred and fused to the sheet of paper, as is well known in the art. After transfer,
conveyor belt 110 moves the copy sheet in the direction of arrow 112 to a drying or
fusing station. The fusing station includes a heated roll 114 and back-up or pressure
roll 116 resiliently urged into engagement with one another to form a nip through
which the sheet of paper passes. The fusing station operates to affix the toner particles
to the sheet of copy substrate so as to bond the multicolor image thereto. Finally,
after fusing, the finished sheet is passed onto a conveyor 118 which transports the
sheet to a chute 120 and guides the sheet into a catch tray 122 for removal therefrom
by the machine operator.
[0023] Generally, after the developed image is transferred from belt 18, residual developer
material tends to remain, undesirably, on the surface thereof. In order to remove
this residual toner from the surface of the belt 18, a cleaning roller 60, typically
formed of an appropriate synthetic resin, is driven in a direction opposite to the
direction of movement of belt 18 for contacting and cleaning the surface thereof.
It will be understood that a number of photoconductor cleaning means exist in the
art, any of which would be suitable for use with the present invention.
[0024] It will be recognized that the foregoing description is directed toward a Recharge,
Expose, and Develop (REaD) process for systematically recharging and re-exposing a
photoconductive member to record latent images thereon, whereby, a charged photoconductive
surface is serially exposed to record a series of latent images thereon corresponding
to the subtractive color of one of the colors of the appropriately colored toner particles
at a corresponding development station, with the different color toner layers being
deposited in superimposed registration with one another on the photoconductive surface
of belt 18. It should be noted that either discharged area development (DAD) techniques,
wherein discharged portions are developed, or charged area development (CAD) techniques,
wherein charged areas are developed, can be employed, as are well known in the art.
[0025] It will also be noted that analogous processes exist for electrostatographically
producing multi-color output prints. Of particular interest with respect to the present
invention is the well-known ionographic-type printing process, wherein latent images
are recorded on a dielectric recording medium. An exemplary printing system of this
type adapted to produce multicolor output prints is shown schematically on FIG. 2.
It will be noted that the system of FIG. 2 is very similar to the system of FIG. 1,
with two important exceptions. First, the recording medium which is embodied as a
photoconductive belt 18 in FIG. 1 is replaced by an electrically insulating or resistive
dielectric material, generally identified in FIG. 2 as belt 17, wherein the dielectric
material is capable of retaining an electrical charge applied thereto. In contrast
to the photoreceptive recording medium of FIG. 1, ionographic recording media typically
possess negligible, if any, photosensitivity which, in turn, provides considerable
advantages, such as: elimination of a requirement for the electrophotographic recording
medium to be maintained in a light impermeable environment; and characteristically
low level of charge decay over time resulting in a substantially constant voltage
profile on the recording medium over an extended time period.
[0026] A second distinction of ionographic type electrostatographic printing systems is
found in the imaging system, whereby the latent image is generated on the recording
medium 17. Once again, in contrast to the photoreceptive charging and subsequent selective
discharge of the photoconductive recording medium described with respect to the system
of FIG. 1, in ionographic systems, latent images are formed by directly depositing
charge in image configuration onto the dielectric recording medium. In one simple
form of ionographic image generation, a linear array of ion emitting devices or ion
heads, are used to apply a surface charge density on the dielectric recording medium
surface for creating a latent electrostatic image thereon. Various alternative imaging
devices are known in the art, such as a writing head having one or more aligned rows
of writing stylus electrodes supported in a dielectric support member opposite, and
in alignment with, an aligned row of backup electrodes, as disclosed, for example,
in U.S. Pat. Nos. 4,042,939 and 4,315,270. It will be apparent to those skilled in
the art that other electrode arrangements for recording a latent image on a dielectric
recording medium may be incorporated in the ionographic type electrostatographic printing
system of FIG. 2.
[0027] Thus, as in the REaD (Recharge, Expose and Develop) process described with respect
to FIG. 1, the ionographic type electrostatographic printing system of FIG. 2, involves
a step in which an electrostatic latent image is formed on a record medium at an imaging
station having a recording head 23, 33, 43 or 53. One version of the recording head
comprises a plurality of recording or writing electrodes physically positioned to
electrically address the dielectric surface of the recording medium as the medium
travels past the image recording head. An aligned series of backup electrodes is also
provided opposite to these writing electrodes forming a printing gap therebetween,
whereby an electrostatic charge is deposited on the dielectric portion of the recording
medium when the potential difference between addressed writing electrodes and the
oppositely opposed backup electrodes is raised to a threshold level, also referred
to as a Passion breakdown point, which may be on the order of several hundred volts.
The timing sequence of energization of the electrodes provides for selective electrical
charging of the dielectric recording medium in image configuration to form the desired
latent image as the recording medium is moved past the imaging head.
[0028] Once the latent image is formed on the dielectric recording medium 17, the steps
of developing the electrostatic latent image to form a visible image thereof may be
identical to, or at least similar to, the development process described with respect
to FIG. 1. Likewise, image transfer and fusing may be carried out using processes
as previously described herein. It will be apparent to those of skill in the art that
any of various systems and processes for carrying out each of the steps of the ionographic
type electrostatographic printing system described herein are known in the art and
may be utilized.
[0029] As previously noted, a significant problem which exists in systems wherein sequential
development steps are conducted over previously developed images in order to produce
a multicolor image arises when developable charge potentials are created due to incomplete
image charge dissipation and/or, generation of non-uniform background potentials due
to the presence of a developed image which tends to elevate the background potential.
These potentials are capable of attracting toner particles during subsequent development
steps, leading to a phenomenon typically known as "overplating" or "staining". It
will be understood that this problem is caused by non-uniform background voltage potentials
on the recording medium after a development and/or recharge and/or imaging cycle,
which, in turn, may be developed by another color in a subsequent development step.
[0030] The present invention contemplates a process and apparatus for preventing image overplating
or staining by systematically selecting development voltage biases for each subsequent
development cycle in a manner which tends to eliminate the circumstances that lead
to overplating. Thus, in accordance with the present invention, a scheme is disclosed
for providing bias voltages to each individual development system present in the overall
multi-color printing system such that the developing bias of a given color is dependent
on the performance of the previous color development and/or recharge and/or imaging
steps.
[0031] In its simplest form, the concept of the present invention is directed toward applying
a predetermined bias to each developer housing for controlling development in the
background areas on the recording medium. Thus, the bias of the development roll is
set to a voltage that is substantially equal to or greater than the charge potential
in the background area. This biasing technique substantially prevents the development
of the background areas, which may include some previous image areas, by the current
development station.
[0032] The change of development due to the change of development bias can be compensated
in a number of ways. For example, an alternative, and more sophisticated embodiment
of the concept of the present invention includes additional similar systematic variation
of image recharge bias voltage for each latent image generating process step in the
multi-color imaging process. In particular, the latent image voltage potential for
any given color image generated on the recording member is selected to be dependent
on the development bias of the previous color. In a preferred embodiment, both image
bias voltage and development bias voltages are controlled in accordance with the development
parameters of the previous color in the multi color process to virtually eliminate
the problem of residual image overplating, thereby maintaining the proper development
of image areas.
[0033] The concept of the present invention will now be described in terms of exemplary
bias voltages applied to each imaging and development station. It will be understood
that in a basic development subsystem, the toner particles in the developing material
obey the basic rule that the force on the toner particles is equal to the product
of the charge and the electrical field such that toner particles are attracted to
the recording medium only when the electrostatic forces acting on the particles is
greater than zero. In a typical electrostatographic printing system, a voltage bias
is applied to a developer system (as represented schematically in FIGS. 1 and 2) so
that a greater potential is required on the recording medium in order to attract the
toner from the developer housing. This practice is utilized to significantly decrease
the amount of toner that develops to non-image or background areas of the recording
medium. Thus, a bias voltage is generally applied to a development system in order
to control background development.
[0034] In accordance with the foregoing explanation, it will be recognized that in a multicolor
electrostatographic system of the type shown and described herein, the bias voltage
applied to the first development station, identified generally by reference numeral
24 is provided strictly for controlling background and image development.
[0035] However, in accordance with the present invention, the bias applied to the subsequent
development subsystem, in this case, developer housing 34, is selectively controlled
in order to prevent the staining or overplating phenomenon. Since the development
bias of the subsequent developer housing is increased to prevent overplating, the
imaging voltage of the associated image must also be increased by substantially the
same amount in order to sustain the development process of that respective color image.
As an example, in the absence of any background potential on the receiving member,
a typical imaging voltage at the second imaging station 32 or 33 may be in the vicinity
of 100 volts while a biasing voltage of 5 volts may be applied to the associated developer
housing 34 for development of the second color. However, if the first image development
recharge and imaging cycle leaves a background potential on the recording medium of
20 volts, the bias voltage applied to the subsequent developer housing is raised to
approximately 25 volts in order to prevent development of that residual image in accordance
with the scheme of the present invention. In turn, the imaging or recharge voltage
used for creating the second image must also be increased in order to maintain the
same voltage differential between that image and the associated developer housing.
In this case, the second imaging station is provided with an electrical bias for creating
an image potential of 120 volts. The same scheme for increasing voltages would be
applied to the subsequent imaging and development subsystems in a manner as described
such that the image voltage at the first imaging station 22 or 23 is less than the
imaging voltage at the second imaging station 32 or 33, which is less than the imaging
voltage at the third imaging station 42 or 43, which, in turn, is less than the voltage
applied to the fourth imaging station 52 or 53. Likewise, the bias voltage applied
to the developer housing 24, is less than the developer bias applied to the developer
housing 34, which is less than the developer bias applied to the developer housing
44 which, in turn, is less than the developer bias applied to developer housing 54.
Most importantly, the developer bias at a given development station is selectively
controlled to be substantially equal to or slightly greater than the background generated
by the development recharge and imaging cycle. This step-up nature of the imaging
and development bias voltages is a unique feature of the present invention.
1. Elektrostatografisches Druckgerät zum Herstellen eines mehrfarbigen Ausgabe-Bildes
aus einem Eingabe-Bildsignal, das umfasst:
ein Aufzeichnungsmedium (18), das so eingerichtet ist, dass eine Vielzahl latenter
elektrostatischer Bilder darauf aufgezeichnet wird, die durch Bild-Ladungspotenzialbereiche
und Hintergrund-Ladungspotenzialbereiche gebildet werden;
eine erste Bilderzeugungseinrichtung (22, 23), die ein erstes elektrostatisches latentes
Bild auf dem Aufzeichnungsmedium erzeugt, das einem ersten Farbauszug des Eingabe-Bildsignals
entspricht;
eine erste Entwicklungsvorrichtung (24), die das erste elektrostatische latente Bild
auf dem Aufzeichnungsmedium entwickelt, indem sie geladenes Entwicklungsmaterial auf
das elektrostatische erste latente Bild aufbringt, um ein erstes entwickeltes Bild
darauf herzustellen;
eine zweite Bilderzeugungseinrichtung (32, 42, 52, 33, 43, 53), die ein zweites elektrostatisches
latentes Bild auf dem Aufzeichnungsmedium erzeugt, das einem zweiten Farbauszug des
Eingabe-Bildes entspricht, wobei das zweite elektrostatische latente Bild über das
erste entwickelte Bild auf dem Aufzeichnungsmedium gelegt wird;
eine zweite Entwicklungsvorrichtung (34, 44, 54), die das zweite elektrostatische
latente Bild auf dem Aufzeichnungsmedium entwickelt, indem sie geladenes Entwicklungsmaterial
auf das elektrostatische zweite latente Bild aufbringt, um ein zweites entwickeltes
Bild darauf herzustellen; wobei das Gerät dadurch gekennzeichnet ist, dass:
es eine Einrichtung zum Einstellen der zweiten Entwicklungsvorrichtung auf eine Spannung
umfasst, die im Wesentlichen dem Ladungspotenzial in den Hintergrundbereichen auf
dem Aufzeichnungsmedium entspricht oder größer ist als diese, um im Wesentlichen Entwicklung
derselben zu verhindern.
2. Elektrostatografisches Druckverfahren zum Herstellen eines mehrfarbigen Ausgabe-Bildes
aus einem Eingabe-Bildsignal, das die folgenden Schritte umfasst:
Bereitstellen eines Aufzeichnungsmediums (18), das so eingerichtet ist, dass eine
Vielzahl latenter elektrostatischer Bilder darauf aufgezeichnet werden, die durch
Bild-Ladungspotenzialbereiche und Hintergrund-Ladungspotenzialbereiche gebildet werden;
Erzeugen eines ersten elektrostatischen latenten Bildes auf dem Aufzeichnungsmedium,
das einem ersten Farbauszug des Eingabe-Bildes entspricht;
Entwickeln des ersten elektrostatischen latenten Bildes auf dem Aufzeichnungsmedium
durch Aufbringen von geladenem Entwicklungsmaterial auf das erste elektrostatische
latente Bild mittels einer ersten Entwicklungsvorrichtung (24), um ein erstes entwickeltes
Bild darauf herzustellen;
Erzeugen eines zweiten elektrostatischen latenten Bildes auf dem Aufzeichnungsmedium,
das einem zweiten Farbauszug des Eingabe-Bildes entspricht, wobei das zweite elektrostatische
latente Bild über das erste entwickelte Bild auf dem Aufzeichnungsmedium gelegt wird;
Entwickeln des zweiten elektrostatischen latenten Bildes auf dem Aufzeichnungsmedium
durch Aufbringen von geladenem Entwicklungsmaterial auf das zweite elektrostatische
latente Bild mittels einer zweiten Entwicklungsvorrichtung (34, 44, 54), um ein zweites
entwickeltes Bild darauf herzustellen; wobei das Verfahren dadurch gekennzeichnet ist, dass:
es das Einstellen der zweiten Entwicklungsvorrichtung während der Schritte der Bilderzeugung
und Entwicklung auf eine Spannung umfasst, die im Wesentlichen dem Ladungspotenzial
in den Hintergrundbereichen auf dem Aufzeichnungsmedium entspricht oder größer ist
als diese, um im Wesentlichen Entwicklung derselben zu verhindern.
1. Machine d'impression électrostatographique destinée à produire une image de sortie
à couleurs multiples à partir d'un signal d'image d'entrée, comprenant :
un support d'enregistrement (18) conçu pour présenter une pluralité d'images électrostatiques
latentes enregistrées sur celui-ci, définies par des zones de potentiel de charge
d'image et des zones de potentiel de charge de fond,
un premier dispositif de formation d'image (22, 23) destiné à générer une première
image latente électrostatique sur ledit support d'enregistrement, correspondant à
une première séparation de couleur du signal d'image d'entrée,
un premier dispositif de développement (24) destiné à développer la première image
latente électrostatique sur ledit support d'enregistrement en déposant un matériau
de développement chargé sur ladite première image latente électrostatique de façon
à produire une première image développée sur celui-ci,
un second dispositif de formation d'image (32, 42, 52, 33, 43, 53) destiné à générer
une seconde image latente électrostatique sur ledit support d'enregistrement correspondant
à une seconde séparation de couleur de l'image d'entrée, ladite seconde image latente
électrostatique étant superposée à ladite première image développée sur ledit support
d'enregistrement,
un second dispositif de développement (34, 44, 54) destiné à développer la seconde
image latente électrostatique sur ledit support d'enregistrement en déposant un matériau
de développement chargé sur ladite seconde image latente électrostatique de façon
à produire une seconde image développée sur celui-ci, ladite machine étant caractérisée en ce que
elle comprend un moyen destiné à régler ledit second dispositif de développement à
une tension qui est sensiblement supérieure ou égale au potentiel de charge dans les
zones de fond sur ledit support d'enregistrement pour empêcher substantiellement le
développement de celles-ci.
2. Traitement d'impression électrostatographique destiné à produire une image de sortie
à couleurs multiples à partir d'un signal d'image d'entrée, comprenant les étapes
consistant à :
fournir un support d'enregistrement (18) conçu pour présenter une pluralité d'images
électrostatiques latentes enregistrées sur celui-ci, définies par des zones de potentiel
de charge d'image et des zones de potentiel de charge de fond,
générer une première image latente électrostatique sur ledit support d'enregistrement,
correspondant à une première séparation de couleur de l'image d'entrée,
développer la première image latente électrostatique sur ledit support d'enregistrement
en déposant un matériau de développement chargé sur ladite première image latente
électrostatique au moyen d'un premier dispositif de développement (24) de façon à
produire une première image développée sur celui-ci,
générer une seconde image latente électrostatique sur ledit support d'enregistrement,
correspondant à une seconde séparation de couleur de l'image d'entrée, ladite seconde
image latente électrostatique étant superposée à ladite première image développée
sur ledit support d'enregistrement,
développer la seconde image latente électrostatique sur ledit support d'enregistrement
en déposant un matériau de développement chargé sur ladite seconde image latente électrostatique
au moyen d'un second dispositif de développement (34, 44, 54) de façon à produire
une seconde image développée sur celui-ci, ledit procédé étant caractérisé en ce que
il comprend le réglage dudit second dispositif de développement durant lesdites étapes
de génération et de développement d'image à une tension qui est sensiblement supérieure
ou égale au potentiel de charge dans les zones de fond sur ledit support d'enregistrement
pour empêcher substantiellement le développement de celles-ci.